At 0° C., 5 ml of benzoyl chloride is added dropwise to 5 g of 15α-hydroxy-18-methyl-4-estrene-3,17-dione in 20 ml of pyridine. After 45 minutes, 2 ml of water is added, the mixture is stirred for another 30 minutes, and then the reaction mixture is poured into ice/water. The thus-precipitated product is suctioned off, dissolved in methylene chloride, washed with water, and dried over sodium sulfate. After chromatography of the crude product on silica gel with an acetone-hexane gradient, 5.6 g of 15α-benzoyloxy-18-methyl-4-estrene-3,17-dione is obtained as a foam.
